A number of system approaches for carrying out airborne exploration for minerals have been contemplated, proposed and practiced heretofore. One system approach of substantial promise has been the use, in a night flying aircraft, of an ultraviolet source to illuminate a target area below the aircraft, the means for sensing any responsive fluorescence in the visible spectrum within the target area. It is well known that many minerals fluoresce in response to stimulation by ultraviolet light, and this principle has been used for many years by geologists and other prospectors carrying hand held instruments at close range to the target.
However, the use of this basic exploration approach in night flying airborne systems, which manifestly offers, theoretically, greatly increased territorial coverage, has not been particularly successful in practice because of the considerable problems of bringing enough ultraviolet energy to bear on a target area of an aircraft and the counterpart problem of somehow sensing the resultant faint fluorescent targets of interest while rejecting other light sources which constitute mere noise and may be overwhelmingly of greater magnitude than the desired target.
Thus, bona fide efforts have been made in the past to realize such an airborne exploration system employing ultraviolet stimulation of fluorescence of desired target minerals. One of the earliest methods employing this system approach is discussed in my U.S. Pat. No. 3,736,428, entitled "Detecting with Ultraviolet Light", issued May 29, 1973. It may be noted that the issuance of this patent was delayed for some years for national security reasons such that the disclosure thereof pertains to work conducted by me in the 1950's. A similar, slightly later system, is disclosed in U.S. Pat. No. 3,043,908 to Madsen, entitled "Fluorographic System for Aerial Surveys", issued July 10, 1962. An improvement to the Madsen system is disclosed in U.S. Pat. No. 3,663,814, entitled "System for Delineating Selective Response of a Material to Radiation in Presence of Visible Illumination", issued May 16, 1972. A more recent patent disclosing a system employing the basic approach of a pulsed ultraviolet source (employing a laser) in conjunction with sensor optoelectronics system is U.S. Pat. No. 4,236,071, entitled "Detection of Uranium by Light Induced Luminescence", issued Nov. 25, 1980, to Chimenti.
None of these systems collect as much data as may be necessary to efficiently carry out the desired exploration for a wide variety of minerals. It is desirable to know the color "signature" of a fluorescing material and the target size. Further, the sensitivity of these prior art systems has been sufficiently low to require, as a practical matter, relatively low level, and hence dangerous, night flying operations. It will therefore be readily apparent to those skilled in the art that it would be highly desirable to provide a mineral exploration system of the class in which airborne exploration may be carried out from a safe height while collecting adequate data to determine the color characteristics, size, and location of fluorescing targets while rejecting, effectively, noise in the form of non-fluorescing or reflected light.